Data storage systems are arrangements of hardware and software that typically include or are coupled to non-volatile data storage devices, such as magnetic disk drives, electronic flash drives, and/or optical drives. Some data storage systems include host interface units (host adapters), disk drives, and disk interface units (disk adapters). A host device (“host”), such as a server computer, desktop computer, laptop computer, or mobile computing device, accesses the data storage of the storage devices in a data storage system by way of host I/O operations that are sent from the host device and received by the data storage system, e.g. through one or more communication channels to the data storage system. The host I/O operations do not address the storage devices of the data storage system directly, but instead access logical volumes of storage that are sometimes referred to as logical disks or “LUNs”. Each logical volume is made up of equal size units of host addressable storage space referred to as “tracks”, each of which may be mapped to a corresponding physical track on one of the non-volatile data storage devices, such as a physical track of disk drive, and into which the host data directed to the track of the logical volume is ultimately stored.
Data storage systems have sometimes created point in time copies of logical volumes referred to as “snapshots”. A snapshot may be created periodically for a logical volume in response to a snapshot timer, and/or in response to a snapshot request received from a host. In order to reduce the overhead required when a snapshot is created, including the overhead resulting from assigning a specific “target” logical volume to a snapshot at the time the snapshot is created, some data storage systems have provided “target-less” snapshots. Target-less snapshots collect the data for a point in time copy of the logical volume for which they are created, but are not initially associated with any target logical volume that can be accessed by a host. Subsequently, when a host requests access to a target-less snapshot, the target-less snapshot must be linked to a target logical volume that can be accessed by the host, so that subsequent accesses by the host to the tracks of the target logical volume provide access to the data in the target-less snapshot, thus allowing the host to access the target-less snapshot through the target logical volume in a conventional manner at the time access to the target-less snapshot is required, while also allowing creation of the target-less snapshot to be performed efficiently without assigning a target logical volume to the target-less snapshot at the time the target-less snapshot is created.